US3586890A - Thermoelectric machines - Google Patents

Abstract

The invention relates to a thermoelectric device including parallel, spaced discs axially of which is provided a plasma chamber with means being included for producing a magnetic field perpendicular to the discs and electrodes for collecting the current generated in the plasma.

Description

Ulllltu Dllbfl l tulle Inventors Georges Klein [56] References Cited 59 bis UNITED STATES PATENTS gan'chude f 76 his 3,215,870 11/1965 Brill 310 1 1 antes, both of Paris, France 3 275 860 9 1966 w 0 3 406 301 10 1968 R ay 31 ll 1 J v a 05a 1 Patented June 22, 1971 Primary ExaminerD. X. Sliney Priority June 13, 1968 Attorney-Edwin E. Greigg France THERMOELECTRIC MACHINES Claims 7 Drawing Figs ABSTRACT: The invention relates to a thennoelectric device US. Cl 310/11 including parallel, spaced discs axially of which is provided a Int.Cl t T H02n 4/02 plasma chamber with means being included for producing a Field of Search 310/1 1' magnetic field perpendicular to the discs and electrodes for 315/1 1 1; 313/231 collecting the current generated in the plasma.

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INVENTORS' GEORGES KLEIN JEAN-CLAUDE DE SIMONE ATTOR NE THERMOELECTRIC MACHINES The invention relates to thermoelectric machines and particularly, but not exclusively, to magnetohydrodynamic generators.

Hall effect magnetohydrodynamic generators have been proposed having a plasma chamber which is defined between two concentric parallel discs. The hot gases constituting the plasma flow radially outwards from a point between the centers of the discs towards their peripheries. A magnetic field perpendicular to the discs is supplied by a coil that is arranged parallel to and concentric with the discs.

At every point in the plasma an electric current of intensity J is generated, the direction of this current being simultaneously perpendicular to the magnetic field and to the direction of motion of the gaseous particles of the plasma at the point concerned. This electric current is thus perpendicular to the radial plane passing through that point. By reason of the circular symmetry of the generator, the resulting current is a loop current, closed on itself and concentric with the generator discs.

Due to the Hall effect, the current with intensity 1,, sets up another current with intensity J,, this second current being perpendicular to the magnetic field and to the direction of the current with intensity J,,. This J, current is thus radial, as is the gaseous flow of the plasma.

The generator has an anode located at its center and a cathode disposed adjacent its periphery. The output voltage of the generator is obtained between these two electrodes.

The discs between which the plasma chamber is located are generally made of a refractory ceramic material. This has cer tain disadvantages, such as the material is difficult to work and is liable to be corroded by the hot gases in the chamber, since these gases are usually charged with particles of the seed material of the plasma.

It has been proposed to pass an electric current through a relatively cold limit layer of gas which is formed adjacent the plasma chamber walls of a magnetohydrodynamic generator by means of bridges of liquid metal, in the form of jets injected at a suitable speed to penetrate the limit layer, each providing a low-impedance path through the layer, and forming an electrode. Both the anode and cathode of the generator comprise a plurality of jets of liquid metal, the distance between corresponding jets in the anode and cathode being such that an electric arc breaks out in the plasma between the rows of jets.

The invention is intended to reduce the disadvantages mentioned above.

In accordance with the invention a thermoelectric machine adapted to exploit the Hall effect has a plasma chamber defined between two concentric parallel discs, as well as means for producing a magnetic field perpendicular to the discs, and electrodes for collecting the current generated in the plasma, each disc being formed of an assembly of sectorshaped cells and each sector-shaped cell comprising an assembly of radially spaced elements arranged substantially perpendicular to the axis of symmetry of the cell-to provide between them gas circulation passageways.

The elements of each sector-shaped cell situated at the same distance from the geometrical center of each disc are preferably assembled to form a member in the shape of a regular polygon, each disc including a number of concentric polygonal members and each side of each polygonal member being formed by one element, the sides of successive polygonal members decreasing in length from the periphery towards the center of the disc.

The thermoelectric machine also suitably includes a device for directing a gas into the gas circulation passageways between the radially spaced elements.

By using the concept taught by this invention it is possible to provide a magnetohydrodynamic generator having a relatively high output power, and a plasma chamber with a relatively long working life, since it is possible to use metal elements in the formation of the discs defining the plasma chamber. Such metal elements are less liable to be corroded by the hot gases of the plasma, particularly when the plasma is seeded with, for example, potassium.

FIG. 3 is a partial view in plan of the generator shown in FIG. 1 showing the radially arranged sector-shaped cells and elements of one disc;

FIG. 4 is a plan view of a sector-shaped cell;

FIG. 5 is a section along the line V-V of FIG. 4;

FIG. 6 is a perspective view of a group of elements of two adjacent radially arranged sector-shaped cells; and

FIG. 7 is a perspective view of the improved MI-ID generator.

Referring now to FIG. I, the plasma chamber of a mag- I netohydrodynamic generator is shown as formed by two concentric parallel discs l-l. A burner 2 is situated at the axial center of the plasma chamber, forming a source of hot ionized gases for the plasma. The generator has two spaced super-conductive coils 3-3 adjacent and parallel to the discs 1-1.

The generator anode is formed by a ring of jets by means of which liquid metal is directed from the periphery towards the interior of the plasma chamber through nozzle means 4-4. The liquid metal is obtained from a reservoir, and passes through the discs [-1 in conduits which are electrically insulated from the discs.

The generator cathode is formed by a ring of jets by means of which liquid metal is directed into the plasma chamber throughnozzles 5. The liquid metal supply arrangements for the cathode are similar to those for the anode.

Each disc is formed from an assembly of sector-shaped cells indicated generally at 8, each comprising a number of metal elements 9 (see FIG. 6).

Referring to FIGS. 2 and 3, the plasma chamber has an outer cylindrical wall 6, in which gas outlet orifices 7 are formed.

FIG. 3 further shows that the face of each element 9 of each sector-shaped cell 8, which is directed towards the interior of the plasma chamber, is trapezoidal. The lengths of the elements decrease from the periphery towards the center of the plasma chamber, and the elements 9 are separated into radially extending groupings. The elements 9 of each sectorshaped cell 8, which are situated at the same distance from the geometrical center of the plasma chamber, are also joined to form a member in the shape of a regular polygon. Each disc is thus constituted of a number of concentric members in the shape of regular polygons, each side of each polygon being formed by one element 9, with the side of the polygons decreasing in length from the periphery towards thecenter of the plasma chamber. The radial separation of the elements 9 provides concentric channels between successive polygonal members.

FIG. 4 shows a plan view of part of one sector-shaped cell 8. FIG. 5 is a cross section taken on the line V-V of FIG. 4.

Referring to FIG. 5, the elements 9 of the sector-shaped cells 8, which are shown in FIG. 4, are supported by heat insulative blocks 12 forming a refractory wall of the disc. The height of the elements 9, measured in the direction perpendicular to the discs I, decreases from the center towards the periphery of the plasma chamber. Thus, a radial cross section through the plasma chamber assumes the form of a divergent duct passing from the interior of the chamber towards its periphery, as shown in FIG. 1.

Each element 9 consists of a head portion 9a and a stem portion 9b. A front face of the head portion 9a forms the trapezoidal surface of the element facing the interior of the plasma chamber, and defining the profile of the plasma chamber. The stem portions 9b are of reduced cross section,

and provide passageways 21 separated from the plasma chamber by narrower passageways 11 between the head portions 9a of adjacent elements 9.

The generator is provided with a device for directing an electrically insulative gas into the channels 21 between successive radially spaced elements 9. The channels Ill and 211 are arranged perpendicular to the direction of flow of the gas particles of the plasma. There is thus relatively little penetration of the plasma into the channels 21 or 111.

FIG. 6 shows the head portions 9a of four elements 9 in each of two adjacent sector-shaped cells. Each head portion 90 has a pipe 14 through which a cooling fluid is circulated. The pipes 14 of the adjacent head portions 90 are joined by external connections 13. The electrically insulative gas directed into the channels 21 between the metal elements 9 is preferably an inert gas. The working life of such an insulation, with voltages greater than or equal to 40 volts, can reach several hundreds of hours. The widths of the channels 21 are of the order of0.3 to 0.4 mm.

Electrical insulation may be similarly provided between the jets of liquid metal of each electrode, blowing orifices being arranged to direct streams of an insulative gas between the individual jets, and parallel to the direction of flow of the liquid metal. The penetration of the insulative gas to the interior of the plasma chamber should be less than the penetration of the jet of liquid metal, to avoid possible obstruction to the passage of the current generated in the plasma chamber.

The liquid metal for the jets is obtained from a reservoir, and a good electrical contact is provided between the liquid metal of the reservoir and one terminal of the generator.

The relatively cold limit layer of air situated adjacent the plasma chamber wall during operation of the generator provides some protection against corrosion of the metal elements 9 by the plasma. Should any of the elements 9 becomeexcessively corroded, or otherwise damaged, they can be easily replaced without disturbing the remainder of the plasma chamber.

The head portions 90: of the metal elements 9 can be maintained at a relatively low temperature of between 200 and 800 C. This relatively low temperature produces the relatively cold limit layer of gas, but the provision of jets of liquid metal penetrating this limit layer enables the current generated in the plasma to be removed with negligible loss in power. The current produced flows between and along two jets of liquid metal, directly reaching the conductors con nected to the generator load. The resistance to passage of the current is mainly purely ohmic, with possibly very small reactive impedances. The ability to extract the current generated with a relatively small power loss, and the opportunity provided by the invention for constructing larger plasma chambers, enables magnetohydrodynamic generators to be realized having relatively high electrical power outputs.

The coils for providing the transverse magnetic field in the plasma chamber are mounted symmetrically, one on the exterior side of each disc. The total axial dimension of the generator is thus relatively low, and the coils are easily accessible. The coils need not necessarily be superconductive coils.

The location of the burner at the center of the plasma chamber enables it to be made sufficiently strong to resist the formed by the jets of liquid metal, the relatively cold limit layer is substantially stable. In magnetohydrodynamic generators having at least partially conductive walls forming the elec trodes, the gas layer adjacent to the partially conductive walls is often unstable. With insulative plasma chamber walls, this layer is stable and is relatively resistant to aerodynamic separation.

Also, in the case of supersonic plasma flow, thejets ofliquid metal forming the cathode c ause recompression shocks in the plasma. This improves the yield of the generator. However, to achieve such recompression shocks the Mach number should not exceed 1.4.

That which we claim is:

l. A thermoelectric device adapted to exploit the Hall effect, comprising a plasma chamber defined between two concentric parallel discs, means for producing a magnetic field perpendicular to the discs, means for producing a radial flow of conductive fluid in the plasma chamber, radially spaced electrode means for collecting the current generated by the Hall effect in the plasma chamber, each disc being formed of an assembly of removable sector-shaped cells, each cell further comprising an assembly of elements arranged substantially perpendicular to the axis of symmetry of the cell and the elements of the cells situated at the same distance from the geometrical center of each disc being assembled to form a member in the shape of a regular polygon having plural side portions, and each disc further including a number of concentric polygonal members, the side portions of which decrease in length from the periphery towards the center of the disc.

2. A device as claimed in claim 1, in which the extension of the elements perpendicular to the planes of the discs decreases from the center of the disc towards its periphery, to thereby define a plasma chamber.

3. A device as claimed in claim 1, in which the elements are adapted to be cooled by a cooling fluid circulated through means defining passages provided within the elements.

4. A device as claimed in claim 3, in which the means defining the passages in said elements are connected.

5. A device as claimed in claim 4, in which the connections between the means defining the passages in the elements are externally thereof.

6. A device as claimed in claim 1, in which said discs include a refractory wall.

7. A device as claimed in claim 1, in which the elements are radially spaced to provide for insulating gas circulation passageways therebetween.

8. A device as claimed in claim 1, in which the means for producing the magnetic field includes two coils.

9. A device as claimed in claim 10, in which the coils are wound with wires of superconductive material.

10. A device as claimed in claim 1, in which each electrode further includes means for directing jets of liquid metal into contact with the conductive fluid in the plasma chamber.

11. A device as claimed in claim 10, in which an anode electrode is formed by a plurality ofjets of liquid metal arranged near the plasma chamber.

12. A device as claimed in claim 11, in which a cathode electrode is formed by a plurality of jets of liquid metal arranged radially outwardly or the plasma chamber.

13. A device as claimed in claim 12, in which the electrodes are arranged in concentric circles.

14. A device as claimed in claim 10, further including means to direct streams of an insulative gas into the plasma chamber.

9 m UNlTED STATES PATENT OFFICE {LU/H3) a CERTlPlCATE 01* CORRELIION Patent No. 5861890 Dated June 22, 1971 Inventor) Georges Klein and Jean-Claude De Simone ml that error appears in the above-identified patent It is certifi reby corrected as shown below:

and that said Letters Patent are he In the Heading it should read --[73] Assignee: Compagnie Generale d Electricite, Paris, France.

In col. 4, line 49, "claim 10" should read --claim 8-- Signed and sealed this 2nd day of November 1971.

(SEAL) Attest:

ROBERT GOTTSCHALK EDWARD M.FLETCHER,JR.

Acting Commissioner of Patents Attesting Officer

Claims (14)

1. A thermoelectric device adapted to exploit the Hall effect, comprising a plasma chamber defined between two concentric parallel discs, means for producing a magnetic field perpendicular to the discs, means for producing a radial flow of conductive fluid in the plasma chamber, radially spaced electrode means for collecting the current generated by the Hall effect in the plasma chamber, each disc being formed of an assembly of removable sector-shaped cells, each cell further comprising an assembly of elements arranged substantially perpendicular to the axis of symmetry of the cell and the elements of the cells situated at the same distance from the geometrical center of each disc being assembled to form a member in the shape of a regular polygon having plural side portions, and each disc further including a number of concentric polygonal members, the side portions of which decrease in length from the periphery towards the center of the disc.

2. A device as claimed in claim 1, in which the extension of the elements perpendicular to the planes of the discs decreases from the center of the disc towards its periphery, to thereby define a plasma chamber.

3. A device as claimed in claim 1, in which the elements are adapted to be cooled by a cooling fluid circulated through means defining passages provided within the elements.

4. A device as claimed in claim 3, in which the means defining the passages in said elements are connected.

5. A device as claimed in claim 4, in which the connections between the means defining the passages in the elements are externally thereof.

6. A device as claimed in claim 1, in which said discs include a refractory wall.

7. A device as claimed in claim 1, in which the elements are radially spaced to provide for insulating gas circulation passageways therebetween.

8. A device as claimed in claim 1, in which the means for producing the magnetic field includes two coils.

9. A device as claimed in claim 10, in which the coils are wound with wires of superconductive material.

10. A device as claimed in claim 1, in which each electrode further includes means for directing jets of liquid metal into contact with the conductive fluid in the plasma chamber.

11. A device as claimed in claim 10, in which an anode electrode is formed by a plurality of jets of liquid metal arranged near the plasma chamber.

12. A device as claimed in claim 11, in which a cathode electrode is formed by a plurality of jets of liquid metal arranged radially outwardly or the plasma chamber.

13. A device as claimed in claim 12, in which the electrodes are arranged in concentric circles.

14. A device as claimed in claim 10, further including means to direct streams of an insulative gas into the plasma chamber.

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